1. Field of the Invention
The present invention relates to a socket for a semiconductor device, having a contact sheet.
2. Description of the Related Art
A semiconductor device mounted for an electronic equipment or others has been subjected to various tests prior to being mounted to the latter so that latent defects are removed. Such tests are carried out in a non-destructive manner including tests in which a voltage stress is applied thereto, or it is operated or stocked in a high temperature environment in correspondence to the thermal and mechanical environmental tests or the like. Of these various tests, a burn-in test in which the operation test is carried out in a high-temperature condition for a predetermined period is particularly effective for removing integrated circuits causing infant mortality failures.
A test jig used for this burn-in test is generally called as an IC socket. As disclosed in a specification of Japanese Patent Application No. 2002-200459 and Japanese Patent Application Laid-open No. 9-017539 (1997), in a test for KGD (Known Good Die) which is a non-defective bare chip passing the preceding test, it is advanced a suggestion that such a bare chip is accommodated in an accommodation portion of the IC socket by a carrier detachably mounted thereto.
As shown, for example, in FIG. 20, the carrier unit is comprised of a carrier housing 2 having a accommodation portion 2A for accommodating a bare chip 12, a contact sheet 6 located on the inner bottom wall of the accommodation portion 2A in the carrier housing 2 via an elastic sheet 4, a pressing cap 14 for pressing an electrode group in the bare chip 12 onto a bump group 6B of the contact sheet 6, and a latch mechanism 10 for selectively holding the pressing cap 14 relative to the carrier housing 2.
The contact sheet 6 has the bump group including a plurality of bumps 6B formed of copper or others opposed to the electrode group in the bare chip 12 to be electrically connected, as shown in FIG. 20. In FIG. 20, two bumps 6B of which are illustrated in an exaggerated manner as representative thereof. The plurality of bumps 6B are arranged in a frame shape in correspondence to the electrode group. A tip end of the respective bump projects from a surface of the contact sheet 6 by a predetermined height level. In this regard, in FIG. 21, of which two bumps 6B are shown as representative of the group thereof for the purpose of simplifying the drawing.
The pressing cap 14 is comprised of a pressing body 16 having a pressing surface to be brought into contact with a surface facing a surface of the bare chip 12 on which the electrode group are formed, a cap body 20 accommodating a base portion of the pressing body 16, and a plurality of springs 18 disposed in a space between the base portion of the pressing body 16 and the inner surface of a recess in the cap body 20, for biasing the pressing body 16 toward the bare chip 12.
The base portion of the pressing body 16 has hooks on the outer periphery thereof and inserted into the recess of the cap body 20 in a movable manner. The cap body 20 has step height 20N on the outer surfaces at opposite ends thereof, with which tip ends of hook members 10FA and 10FB of the latch mechanism 10 are engaged, as shown in FIG. 20.
The latch mechanism 10 is comprised of the hook members 10FA and 10FB supported rotational moveably by the carrier housing 2 to be engageable with the step height 20N of the cap body 20 in the pressing cap 14, and helical torsion springs (not shown) for biasing the hook members 10FA and 10FB in the direction that they are engaged with the step height 20N of the cap body 20.
Accordingly, when the pressing cap 14 is located over the bare chip 12 positioned in advance relative to the bumps 6B of the contact sheet 6, as shown in FIG. 21, the tip ends of the hook members 10FA and 10FB of the latch mechanism 10 are made to rotate by the edge of the step height of the cap body 20 of the pressing cap 14 to be away from each other so that the pressing body 16 of the pressing cap 14 is accommodated in the accommodation portion 2A.
When the pressing cap 14 is mounted to the interior of the accommodation portion 2A in the carrier housing 2, the outer periphery of the pressing body 20 is guided by a guiding member 8 provided in the carrier housing 2. Thereafter, by being biased by the helical torsion spring, tip ends of the hook members 10FA and 10FB of the latch mechanism 10 is made to rotate in the mutually approaching direction as shown in FIG. 20 and engaged with the upper surfaces of the step height 20N of the cap body 20. As a result, the pressing cap 14 is held by the carrier housing 2.
Since the respective bump 6B as described above is formed with diameter-to-height ratios of 1:1, if the diameter becomes smaller in correspondence to the high-density arrangement of the electrode group in the bare chip 12, the height of the bump 6B is also lower.
Accordingly, when a region in the vicinity of the bump group opposed to the elastic sheet 4 in the contact sheet 6 sinks against the elasticity of the elastic sheet 4 as shown in FIG. 22 in an partially enlarged manner, there is a risk in that the outer peripheral edge of the bare chip 12 is brought into contact with a copper conductor layer 6C formed on the surface of the contact sheet 6 and may be damaged thereby, as shown in FIG. 21. Also, there is a risk in that a contact pressure of the bump group of the contact sheet 6 with the electrode group of the bare chip 12 is lower than a predetermined value.
FIG. 23 illustrates another example of the conventional carrier unit. The carrier unit shown in FIG. 23 is comprised of a carrier housing 2′ having an accommodation portion 2A′ for accommodating a bare chip 12′, a contact sheet 6′ disposed on the inner bottom of the accommodation portion 2A′ of the carrier housing 2′ via an elastic sheet 4′, a pressing cap 14′ for pressing the electrode group in the bare chip 12′ onto the bump group of the contact sheet 6′, and a latch mechanism 10′ for selectively holding the pressing cap 14′ on the carrier housing 2′.
The contact sheet 6′ has a plurality of bumps 6b′ made of copper or others and opposed to the electrode group in the bare chip 12′ to be electrically connected thereto. In this regard, in FIG. 23, of which two bumps 6b′ are shown in an exaggerated manner as representative. A tip end of the respective bump 6b′ projects from the surface of the contact sheet 6 by a predetermined height.
The pressing cap 14′ is comprised of a pressing body 16′ having a pressing surface to be brought into contact with a surface of the bare chip 12′ opposite to the surface of the bare chip 12′ on which the electrode group are formed, a cap body 20′ for accommodating a base portion of the pressing body 16′ and a plurality of springs 18′ disposed in a space between the base portion of the pressing body 16′ and the inside surface of the cap body 20′, for biasing the pressing body 16′ toward the bare chip 12′.
The base portion of the pressing body 16′ is inserted into a recess of the cap body 20′ in a movable manner, and has hooks on the outer periphery thereof.
The cap body 20′ has projections at opposite ends thereof to be engaged with hook members 10′ of the latch mechanism.
The latch mechanism includes hook members 10′ supported rotational moveably by the carrier housing 2′ to be engageable with the projections of the cap body 20′ in the pressing cap 14′, and helical torsion springs for biasing the hook members 10′ in the direction that they engage with the projections of the cap body 20′.
Accordingly, when the pressing cap 14′ is located over the bare chip 12′ positioned in advance relative to the bumps 6b′ in the contact sheet 6′, tip ends of the hook members 10′ of the latch mechanism are made to rotate by the slanted surface of the projection of the cap body 20′ in the pressing cap 14′ in the mutually parting direction, whereby the pressing body 16′ of the pressing cap 14′ is accommodated. When the pressing cap 14′ is mounted into the accommodation portion 2A′ of the carrier housing 2′, the outer periphery of the cap body 20′ is guided by guide members 8′ provided at the carrier housing 2′. Thereafter, by the biasing force of the helical torsion springs, the tip ends of the hook members of the latch mechanism 10′ are made to rotate in the mutually approaching direction and engage with the upper surface of the projection of the cap body 20′. As a result, the pressing cap 14′ is held by the carrier housing 2′.
The carrier unit, the bumps 6b′ in the contact sheet 6′ or others are preferably durable against the repeated use of several times. Particularly, by the repeated use, a contact area between the tip end of the bump 6b′ in the contact sheet 6′and the electrode of the bare chip 12′ will be liable to be gradually larger because the bare chip 12′ is pressed at a predetermined pressure.
As described above, the cap body 20′ of the pressing cap 14′ is mounted to the accommodation portion in the carrier housing 2′ while being guided by the guide member 8′ provided in the carrier housing 2′. However, since a gap is actually formed between the outer periphery of the carrier housing 2′ and the guide member 8′, the tip ends of the bumps 6b′ are pressed by a deviated pressure generated on the chip 12′ by the pressing cap 14′ inclined toward one side.
Accordingly, the distribution of heights and contact areas or the like of the plurality of bumps 6′ is varied to exceed the allowable value, whereby there is a risk in that the electric connection the tip ends of a portion among the bumps 6b′ with the electrodes of the bare chip 12′ becomes unreliable.